Electromagnetic radiation, for example X-ray radiation, is used to examine the contents of luggage and parcels prior to allowing such items to be taken on or loaded on transport vehicles or before allowing entry into buildings or other facilities. X-ray scanning machines continuously convey luggage, parcels, cargo, and personal items that are exposed to X-ray radiation that can penetrate the container and can be used to create an image of the contents of the container. Packages and luggage of all shapes and sizes are accommodated by the same scanning system.
Radiation is contained within the scanning system by shielding curtains disposed at the entrance and exit of the scanning system. Conventional shielding curtains are fabricated in a laminated construction. Rolls of material scrim, lead vinyl, lead rubber, and Teflon/nylon are fed from rolls and each becomes a layer of a thin sheet of material. The lead vinyl is sandwiched between Teflon/nylon layers. The continuous strip is wound on a spool and then cut into individual strips. The individual strips are then secured by one or two metal bars or attachment devices and arranged adjacent to each other such that a series of parallel individual strips hang in front of an entrance or exit of the scanning machine and collectively contain or deflect the X-rays within the machine, such that workers are not exposed to potentially harmful X-rays. The lead content of the strips is selected to block the radiation generated in a particular application. The layered construction of the curtain strips forms uniform thickness strips that are free of surface texture.
Sandwiching the individual strips of layered construction between two generally flat bars forms the X-ray shielding curtain. Each of the bars includes a plurality of through holes. A fastener is received through the front bar, and extends through a hole formed through the layered strip, and through the rear bar or attachment bar located on the X-ray scanning system. The holes in the layered construction strips are generally formed after the strips are constructed but before the strips are sandwiched between the clamping bars. Misplacement or misalignment of an individual curtain strip with respect to an adjacent curtain strip may lead to unwanted radiation leakage through a curtain bank.
An example scanning system is disclosed in U.S. Pat. No. 4,020,346, issued on Apr. 26, 1977, entitled “X-Ray Inspection Device and Method,” which is hereby incorporated by reference. The '346 patent discloses a scanning system with two banks of shielding arranged parallel to each other to block the entrance to the scanning system, and two banks of shielding curtains arranged parallel to each other to block the exit to the scanning system. However, scanning systems for different applications, such as pre-shipping parcel or cargo inspection may have greater strength radiation, and therefore may have additional banks of radiation shielding curtains positioned at the entrance and exit.
Parcels, luggage, or personal items that are conveyed through the scanning system displace the strips of curtains. In certain applications, a light parcel may be required to simultaneously displace two or more banks of curtains. If the parcel is too light to displace multiple curtain banks, a back-up may occur on the system that must be addressed by a worker. As should be obvious, curtains with a greater stiffness are not as easily displaced as curtains that are more flexible. Also, friction between the curtains and the parcel must be overcome so the parcel can move through the scanning system. Finally, the layered construction strip curtains wear, which can lead to unwanted material, including lead, being rubbed off onto the luggage or parcels. Of course, worn shielding curtains need to be replaced.